Various types of color display technologies are known in the art. For example, there are CRT display systems, LCD systems, and projection display systems. In front projection displays, the projected images are viewed from a reflective viewing screen. In rear projection displays, the projected images are viewed through a transmissive viewing screen.
To produce color images, existing display devices use three primary colors, typically, red green and blue, collectively referred to as RGB. In simultaneous projection display systems, the three primary color components of the image are modulated and displayed simultaneously using one or more Spatial Light Modulators (SLMs).
Three primary projection displays implementing color selective retarder stack technology, e.g., as manufactured by Colorlink Incorporated, 2477 55th St., Boulder, Colo., 80301, USA, are described in “LCoS projection color management using retarder stack technology”; Gary Sharp, Michael Robinson, Jianmin Chen, Jonathan Birge; Elsevier Science Volume 23, 2002, pp 121-128 (Reference 1), the entire disclosure of which is incorporated herein by reference.
FIG. 1 schematically illustrates an optical configuration 100 of a RGB projection device implementing three transmissive reflective Liquid Crystal Display (LCD) panels to produce a color image, as described in Reference 1.
The light from a lamp (not shown) passes through an input polarizer 101 to obtain an s-polarized white light beam. Polarizer 101 typically includes a polarization conversion system followed by a clean up Polarized Beam Splitter (PBS), a sheet polarizer, or a wire-grid polarizer, as are known in the art.
An input green/magenta filter 102 rotates the polarization, e.g., from s-polarization to p-polarization, of a green part of the spectrum of the light received from polarizer 101. The s-polarization of other parts of the spectrum may be maintained.
Configuration 100 also includes a PBS 103 to transmit p-polarized light, e.g., the green light received from filter 102; and to reflect the remaining part of the light, as is known in the art. The light reflected by PB S103 may include blue, red, and inter-primary light.
Configuration 100 also includes a single layer retarder 104. Retarder 104 may have half-wave retardation in the green and zero-orientation, for correcting skew rays, as is known in the art. Retarder 104 may enhance throughput of the green light.
Configuration 100 also includes a PBS 105, a retarder 106, and a reflective LC spatial light modulator 107. PBS 105 transmits the p-polarized green light received from retarder 104 towards retarder 106. Retarder 106 may include a skew-ray correcting 0-oriented retarder with quarter-wave retardation in the green spectrum. Modulator 107 may modulate and reflect the green light received from retarder 106, while rotating the polarization of the reflected light, e.g., back to s-polarization. PBS 105 may reflect the s-polarized green light towards a single layer retarder 108. Retarder 108 may have half-wave retardation in the green and zero-orientation, for correcting skew rays. Retarder 108 may enhance contrast.
Configuration 100 also includes a Red-Blue ColorSelect™ filter 112 to rotate the polarization, e.g., from s-polarization to p-polarization, of a red part of the spectrum of the light reflected by PBS 103, while maintaining the s-polarization of the blue part of the spectrum. Filter 112 may function as a zero-oriented half-wave retarder in the blue spectrum, and a π/4 oriented half-wave retarder in the red spectrum, e.g., in order to compensate for skew-ray.
Configuration 100 also includes a PBS 113, two reflective LC spatial light modulators 114 and 115, and a Red/Blue ColorSelect™ filter 116. PBS 113 may transmit the p-polarized red light received from filter 112 towards modulator 115, and reflect the s-polarized blue light towards modulator 114. Modulator 114 may modulate and reflect red light received from PBS 113, while rotating the polarization of the reflected light, e.g., back to s-polarization. Modulator 115 may modulate and reflect blue light received from PBS 113, while rotating the polarization of the reflected light to p-polarization. PBS 113 may reflect the s-polarized red light towards filter 116. PBS 113 may also transmit the p-polarized blue light towards filter 116. Filter 116 may rotate the polarization, e.g., from s-polarization to p-polarization, of the red light received from PBS 113, while maintaining the p-polarization of the blue light.
Configuration 110 also includes a combining PBS 109 to combine the red, blue, and green light beams, by transmitting the p-polarized red and blue light beams towards a filter 110; and reflecting the s-polarized green light beam towards filter 110. Filter 110 includes a green/magenta filter to transmit primary blue and red-p-polarized light, while rotating the polarization of the primary green and inter-primary bands back to p-polarization.
Configuration 100 also includes a clean-up polarizer 111 to enhance contrast, and block inter-primary bands.
It will be appreciated by those skilled in the art, that in order to achieve desired green color coordinates, filter 102 has a parallel-polarizer blocking band that captures only a part of a green-yellow spectrum of the white light.